This invention relates to a process for mono-chlorinating paraffins. More particularly, the invention pertains to a process for the purification of recycled paraffins in a mono-chlorination process.
The photochlorination of paraffins to form alkyl chlorides is well known in the art. Thus, Sconce et al. U.S. Pat. No. 2,492,941 discloses a process for the complete chlorination of hydrocarbons by first treating a partially chlorinated hydrocarbon, such as chloropropane, with alkali metal and alkaline earth hydroxides or alkali metal carbonates, and then chlorinating the treated material to obtain ochtachloropropane. Stretton et al. U.S. Pat. No. 2,916,428 discloses a process for making a chlorinated wax product having a high chlorine content and other desired properties by chlorinating a waxoil feed mixture containing a major proportion of a soft paraffin wax and minor proportion of a hydrocarbon oil. The chlorinated wax product of Stretton et al. is said to be useful in the preparation of mastic floor and wall tiles. In Hurley et al. U.S. Pat. No. 3,418,388 there is disclosed a process for chlorinating normal paraffins and then alkylating benzene with the resultant alkyl chlorides to produce an alkly benzene mixture, which may be used to produce a detergent by sulfonation. The process of Hurly et al. favors the formation of secondary normal alkyl chlorides by conducting the photochlorination reaction while the normal paraffins are dissolved in benzene. Contrary to the Hurley et al. disclosure, McCoy U.S. Pat. No. 3,948,741 discloses a chlorination process favoring the formation of terminally substituted alkanes, which are said to be valuable chemical intermediates in the production of fatty acids, amines, and sulfonates for use as detergents, etc. The method of McCoy consists of chlorinating a mixture of a normal paraffin hydrocarbon and a diluent-solvent of a chlorinated or fluorinated aliphatic hydrocarbon.
As indicated in the Hurley et al. patent, normal alkyl mono-chlorides are useful in the alkylation of benzene with subsequent sulfonation to produce a detergent, while alkyl polychlorides will react with the benzene to form undesirable diphenyl alkanes. To favor the production of alkyl mono-chlorides while suppressing the formation of alkyl polychlorides, the photochlorination reaction is normally conducted at a rate such that only about 20 to 30 mole percent of the normal paraffins starting material has been chlorinated. This procedure results in a large amount of unreacted normal paraffins which must be recycled to the photochlorination reactor to make the process commercially feasible. It has been found that when such large amounts of the unreacted normal paraffins are to be recycled and combined with fresh normal paraffins for feeding to the photochlorination reactor, the photochlorination reaction is sometimes retarded and the entire process upset.
It is, accordingly, an object of the present invention to provide an improved process for the photochlorination of normal paraffins in which the recycling of a large proportion of the paraffins would not retard the photochlorination reaction. It is another object of the invention to provide an improved photochlorination process in which certain undesirable impurities are removed from unreacted paraffins before they are recycled to the photochlorination reactor. These and other objects of the invention will become apparent from the following description.